Cobalt oxide (assigned
as CoO
x
) is
an efficient oxygen evolution reaction (OER) nanocatalyst, which has
been extensively studied as a replacement to noble metal-based catalysts.
The recent observations and understandings for the interfacial state,
adsorbed intermediate products, and rate-determining steps (RDS) on
CoO
x
, however, have remained elusive because
of the dynamic transformation of different Co ions and the transient
nature of the intermediates formed during the OER process. In this
work, we propose that under the chosen experimental conditions, the
redox process between Co(III) and Co(IV) species does not follow a
proton-coupled electron transfer mechanism that is thought to be common
prior to the OER, but it involves a proton-decoupled electron transfer,
clarified by isotope labeling experiments and in situ electrostatic modulation. The interfacial state of CoO
x
is negatively charged prior to the formation of
Co(IV)O species. The theoretical concentration of the resulting
Co(IV)O species is approximately 0.1229 × 1019 cm–2. The Co(IV)O species are demonstrated
to directly regulate the OER performance. Moreover, we experimentally
monitor the dynamic evolution behaviors of Co(IV)O, Co(O)O–, OOH*, and O2
–* intermediates
during the OER with in situ time-resolved infrared
spectroscopy, and the following elementary step OOH* + OH– → OO–* + H2O is likely to be
the unexpected RDS in the OER process.
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